The present invention relates to an inductive energy transfer system for supplying energy from a stationary primary rail to a number of movable secondary rails each connected to a movable unit. The system is particularly suited for conveyor units of a sorter system, each unit having article-supporting means, the energy provided from the energy transfer system being used primarily for discharging articles from the article-supporting means.
In particular, the invention relates to a system in which the primary rail as well as the secondary rails are provided with legs so that the legs in an operational position are overlapping so as to reduce the losses caused by the air gap between the primary rail and the secondary rails.
It is known from the prior art to transfer energy between a stationary part and one or more movable parts by means of inducting a current in a secondary coil on a movable part with a magnetic field generated by applying an actuating current in a primary coil on the stationary part.
The primary side of known inductive energy transfer systems typically comprises a single conductor that is more or less fully encircled by a rail or screen carrying the secondary coil of the secondary side and formed from a magnetic conductive material. The part carrying the secondary coil may be a ferrite core which is particularly suited as a magnetic conductive material. The supply unit for supplying power to the primary coil is commonly equipped with compensating means for providing compensation for rapidly changes in the loads on the primary coil from the secondary coils.
In order to improve the usefulness of inductive energy transfer, in particularly for systems with minor loads on the primary rail but also applicable to systems with larger loads, it is important the inductive energy transfer system is technically stable and reliable and is economically sound with respect to initial costs, installation as well as in operation.
It is an object of the present invention to provide an inductive energy transfer system in which the losses caused by the air gap between the primary coil and the secondary coil(s) are reduced.
It is a further object of the present invention to provide a system in which the temporal variations in the loads on the primary coil from the secondary coil(s) are reduced.
It is a yet further object of the present invention to provide a system in which the losses in the energy transfer are reduced and the efficiency thus is increased.
These and other objects of the present invention that will become apparent from the following description are fulfilled by means of the invention as disclosed below.
Thus, the present invention concerns a sorter for conveying and sorting articles comprising
a guide rail forming a closed loop,
a U-shaped primary rail made from a magnetic conducting material and having a primary coil connected to a power supply unit for generating an actuating current in the primary coil, the primary rail being positioned along at least a part of the guide rail, and
a plurality of movable units moving along said guide rail, each unit having article-supporting means defining at least one article-supporting surface, means for discharging articles from said surface and a U-shaped secondary rail made from a magnetic conducting material and having a secondary coil, the secondary rail being so positioned during operation that the legs of the primary rail and the legs of the secondary rail overlap over a substantial part of the secondary rail in the direction of motion of the unit, the overlap being of at least twice the distance between the leg in question of the primary rail and the corresponding leg of the secondary rail, the unit having means for using energy inducted in the secondary coil for driving the means for discharging articles.
The overlap is in the embodiment shown in FIG. 1 of about four times the distance between the legs defining the air gap the magnetic flux has to pass. The longer the overlap the lower the losses, but the air gap must from a practical point of view have a minimum size and the length of the overlap is restricted by the length of the legs of the rails. A realistic ratio of the overlap and the air gap is from the practical point of view between 1 and 10, preferably from 2 to 6 with 4 as a suitable level.
The length of the secondary rails in the direction of motion of the unit depends of cause on the size of the units and the spacing between consecutive units but between 0.1 m and 1 m are reasonable for most applications, preferably between 0.15 m and 0.3 m.
It is an advantage that the secondary rails are arranged with a minor gap in the longitudinal direction of the primary rail between consecutive secondary rails so as to improve the efficiency of the system. The secondary rails should therefore cover from 30% to 95% of the primary rail in the longitudinal direction of the primary rail. In preferred embodiments are 50%-65% of the primary rail covered which has proven to be sufficient to ensure a satisfactory efficiency although the efficiency will be further improved if about 95% of the primary rail is covered, which is a maximum from a practical point of view if mutual motion of consecutive secondary rails is to be allowed for.
The present invention may be used to provide power directly from the secondary coil to power consuming devices on the movable units, a so-called direct drive. However, the actuating current in the primary coil may be skewed or disturbed if these devices have a high power consumption resulting in disturbances in the remaining movable units having a secondary coil and possibly to a decrease of efficiency of the energy transfer system.
Thus, in a preferred embodiment of the present invention, the movable units comprise energy storage means for storing energy inducted in the secondary coil, in particular an electric battery but the energy may be stored by means of other storage means, such as one more capacitors. The variable power consumption of the means for discharging articles from the article-supporting surface is in this way smoothened so that the mean energy transfer to a unit when the primary rail and the secondary rail are in an operational position is low, typically a current between 200 and 1000 mA and preferably between 400 mA and 800 mA at a voltage of between 5 VAC and 30 VAC, preferably between 10 VAC and 20 VAC, such as about 16 VAC, which after rectifying becomes a voltage of 12-14 VDC. The smoothening of the power consumption means that the transferred power is low and substantially constant for which reason the energy transfer system may be constructed simple and without means for compensating for rapid changes in the load on the primary side of the system.
According to an alternative embodiment of the invention, two or more units are electrically connected and share a common energy storage means.
The sorter may advantageously comprise a shield made from a non-ferromagnetic, electrically conducting material, the shield substantially encircle the outer of the primary rail at a distance less than the distance between the leg of the primary rail and the corresponding leg of the secondary rail. The shield may closely adjacent to the primary rail and partly or completely in abutting contact with the primary rail. The shield is in a preferred embodiment mainly made from aluminium.
Furthermore, the secondary rail may be provided with a middle leg carrying the secondary coil, the primary coil being in this case arranged so that a first part of at least one winding of the primary coil passes between a first leg of the secondary rail and the middle leg and a second part of the at least one winding carrying the return current of the first part passes between a second leg of the secondary rail and the middle leg.
The primary coil may be arranged within the primary rail and be carried by holding means made from a non-ferromagnetic material.
The article-supporting means of the movable units comprise in a preferred embodiment of the present invention an endless belt defining the article-supporting surface, the belt being movably arranged and having means for moving the belt so as to discharge articles carried by the belt. The means for moving the belt is power supplied by means of the secondary coil. Preferably, the belt is movably arranged in a direction substantially perpendicular to the direction of motion of the unit.
According to an alternative embodiment of the present invention comprise the article-supporting means of the movable units a tray that is arranged so that it may be tilted about an axis that is substantially parallel to the direction of motion of the unit by means of a tilt mechanism that is supplied with power from the secondary coil. Articles supported by the article-supporting surface defined by the tray may thus be discharged in a direction being substantially perpendicular to the direction of motion of the unit.
The power supply unit for generating the actuating current in the primary coil comprises in a preferred embodiment of the present invention means for impressing a pulsed actuating voltage onto the primary coil which forms part of a tuned resonance circuit comprising a capacitor and the power supply unit further comprises means for measuring the magnitude of the generated current in the primary coil and adjusting the pulse-width of the actuating voltage in order to achieve a predetermined magnitude of the generated current.
Alternatively or additionally, the power supply unit may, apart for means for impressing a pulsed actuating voltage onto the primary coil which forms part of a tuned resonance circuit comprising a capacitor, further comprise means for successively changing the frequency of the actuating voltage within a predetermined frequency range and means for determining the temporal relation between the pulses of the actuating voltage and the phase of the generated current so as to determine the resonance frequency of the tuned resonance circuit.
The above-described power supply unit constitutes, when applied to an inductive energy transfer system, an invention in itself. Likewise, the above-described inductive energy transfer system constitutes an invention in itself, whether or not it is applied to a sorter.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.